2roa: Difference between revisions

[[Image:2roa.jpg|left|200px]]

'''Solution structure of calcium bound soybean calmodulin isoform 4 N-terminal domain'''

The intracellular calcium ion is one of the most important secondary messengers in eukaryotic cells. Ca2+-signals are translated into physiological responses by EF-hand calcium binding proteins such as calmodulin (CaM). Multiple CaM isoforms occur in plant cells, while only a single CaM protein is found in animals. Soybean CaM isoform 1 (sCaM1) shares 90% amino-acid sequence identity with animal CaM (aCaM), whereas sCaM4 is only 78% identical. These two sCaM isoforms have distinct target-enzyme activation properties and physiological functions. sCaM4 is highly expressed during the plant's self-defense reaction, and activates the enzyme nitric-oxide synthase (NOS), while sCaM1 is incapable of activating NOS. The mechanism of selective target-activation by plant CaM isoforms is poorly understood. We have determined high resolution NMR solution structures of Ca2+- sCaM1 and Ca2+-sCaM4 by utilizing nuclear-Overhauser-effects and residual dipolar couplings. These were compared to previously determined Ca2+-aCaM structures. For the N-lobe of the protein, the solution structures of Ca2+-sCaM1, Ca2+-sCaM4 and Ca2+-aCaM all closely resemble each other. However, in spite of the high sequence identity with aCaM, the C-lobe of Ca2+-sCaM1 has a more open-conformation and consequently a larger hydrophobic target-protein binding pocket than Ca2+-aCaM or Ca2+-sCaM4, the presence of which was further confirmed through biophysical measurements. The single Val144 Met substitution in the C-lobe of Ca2+-sCaM1, that restores its ability to activate NOS, alters the structure of the C-lobe to a more closed-conformation resembling Ca2+-aCaM and Ca2+-sCaM4. The relationships between the structural differences in the two Ca2+-sCaM isoforms and their selective target-activation properties are discussed.

2ROA is a [[Single protein]] structure of sequence from [http://en.wikipedia.org/wiki/Glycine_max Glycine max]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=2ROA OCA].